1. Field of the Invention
The present invention relates to a process pretreatment of metal-plating a resin molded article formed from a resin composition containing as main components a polyphenylene sulfide and a glass-reinforcing agent (filler). More detailedly, the invention relates to a process which comprises pretreating the above resin molded article and then metal-plating the resultant resin molded article to obtain a resin molded article having a high peel strength of the metal plated layer as well as an excellent smoothness of the surface.
2. Prior Art
Polyphenylene sulfide (hereinafter sometimes abbreviated as "PPS") is known as a resin excellent in heat resistance, solvent resistance, electric characteristics, mechanical strength, dimensional stability, flame retardancy, etc., and has recently received attention. Particularly, this PPS resin can further be improved in the above performances by conjugation with a fibrous reinforcing agent such as glass fiber and carbon fiber or with an inorganic filler such as talc, clay and silica, and the resultant improved resins are widely used as electric parts, electronic parts, mechanical structural parts, etc. On the other hand, based on its excellent solder heat resistance, dielectric characteristic and the like, use development of PPS resin as a material for printed circuit boards, three dimensional molded printed circuit boards has also been progressed. It is considered that metal plating is indispensable for PPS resin molded articles to be utilized for these uses. However, since PPS resin is excellent in chemical resistance, the resin is extremely hard to be chemically etched and when metal-plating is made, it is difficult to obtain a sufficient peel strength of the metal. Thus, there has been developed and proposed treating liquids for chemically etching, before metal plating, molded articles of PPS resins or reinforced PPS resin compositions. For example, a process is known which comprises etching a molded article of a PPS resin, particularly a glass fiber-reinforced PPS resin composition, with nitric acid alone or a mixed liquid of nitric acid and hydrofluoric acid (Japanese Laid-Open Patent Publication No. 54290/1984). Because this known process includes a severe treatment for obtaining a sufficient peel strength of the metal plated layer the glass reinforcing agent contained in the PPS resin is completely dissolved and removed. As a result, unevenness of the plated surface becomes extremely large and appearance thereof also becomes bad. When a plated product is used in preparation of a printed circuit board by resist pattern formation, electroplating or the like or a three dimensional molded printed circuit board, it has become a large obstacle and practical problem that unevenness of the plated surface is thus large and surface smoothness is insufficient.